Critical speed, D’ and pacing in swimming: Reliability of a popular critical speed protocol applied to all four strokes

Abstract Purpose: The validity of the critical speed (CS) concept has been investigated in front crawl swimmers using protocols involving multiple performance trials. The reliability and practical feasibility of CS protocols with strong face validity remain unknown in all four swimming strokes. This study aimed to assess reliability and practical feasibility of a widely used CS protocol in all four strokes. Methods: 32 national-level swimmers (butterfly n=7, 19 ± 2 years old; backstroke n=8, 18 ± 2 years old; breaststroke n=7, 18 ± 2 years old; front crawl n=10, 17 ± 2 years old) performed three 200-m and three 400-m performance trials in their specialist stroke over a three-week period. CS and supra-CS distance capacity (D’) were modelled from the linear relationship between distance and time. At the end of the three weeks, all swimmers were asked whether they felt they could or would want to complete an 800-m performance trial as part of a CS protocol. Results: CS derived from 200-m and 400-m performance trials is reliable (typical error ≤ 0.04 m.s-1; coefficient of variation < 4% for all strokes) while D’ is not (typical error between 4 to 9 m; coefficient of variation 13-45%) . Response rate to the follow-up questions was 100%. Only a few butterfly swimmers would want to (14%) or felt they could (29%) complete an 800-m performance trial with more positive responses for breaststroke (57% and 71%), backstroke (75% and 100%), and front crawl swimmers (90% and 100%).Conclusion: Using 200-m and 400-m performance trials is a reliable and practical method for determining CS in backstroke, breaststroke and front crawl swimmers. Including an 800-m performance trial would not be practical with butterfly swimmers, would be challenging with breaststroke swimmers, but would be feasible with front crawl and backstroke swimmers.